From d6be3a4e96fcf8e5397485617be90e51d47a25b7 Mon Sep 17 00:00:00 2001
From: Akshay Dubey <38462415+itsAkshayDubey@users.noreply.github.com>
Date: Wed, 30 Nov 2022 16:50:38 +0530
Subject: [PATCH] algorithm: Hexagonal number (#1265)

---
 Maths/HexagonalNumber.js           | 21 +++++++++++++++++++++
 Maths/test/HexagonalNumber.test.js | 19 +++++++++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 Maths/HexagonalNumber.js
 create mode 100644 Maths/test/HexagonalNumber.test.js

diff --git a/Maths/HexagonalNumber.js b/Maths/HexagonalNumber.js
new file mode 100644
index 0000000000..31fac7ea75
--- /dev/null
+++ b/Maths/HexagonalNumber.js
@@ -0,0 +1,21 @@
+/*
+ * Author: Akshay Dubey (https://github.com/itsAkshayDubey)
+ * Hexagonal Number: https://en.wikipedia.org/wiki/Hexagonal_number
+ * The nth hexagonal number hn is the number of distinct dots in a pattern of dots
+ * consisting of the outlines of regular hexagons with sides up to n dots, when the
+ * hexagons are overlaid so that they share one vertex.
+ */
+
+/**
+ * @function hexagonalNumber
+ * @description -> returns nth hexagonal number
+ * @param {Integer} number
+ * @returns {Integer} nth hexagonal number
+ */
+
+export const hexagonalNumber = (number) => {
+  if (number <= 0) {
+    throw new Error('Number must be greater than zero.')
+  }
+  return number * (2 * number - 1)
+}
diff --git a/Maths/test/HexagonalNumber.test.js b/Maths/test/HexagonalNumber.test.js
new file mode 100644
index 0000000000..ebfc1cc738
--- /dev/null
+++ b/Maths/test/HexagonalNumber.test.js
@@ -0,0 +1,19 @@
+import { hexagonalNumber } from '../HexagonalNumber'
+
+const expectedValuesArray = [1, 6, 15, 28, 45, 66, 91, 120, 153, 190, 231, 276, 325, 378, 435, 496, 561, 630, 703, 780, 861, 946]
+
+describe('Testing hexagonalNumber', () => {
+  for (let i = 1; i <= 22; i++) {
+    it('Testing for number = ' + i + ', should return ' + expectedValuesArray[i], () => {
+      expect(hexagonalNumber(i)).toBe(expectedValuesArray[i - 1])
+    })
+  }
+
+  it('should throw error when supplied negative numbers', () => {
+    expect(() => { hexagonalNumber(-1) }).toThrow(Error)
+  })
+
+  it('should throw error when supplied zero', () => {
+    expect(() => { hexagonalNumber(0) }).toThrow(Error)
+  })
+})